Because electrical and electronic components generate heat during use, heat removal is generally necessary in order to allow these components to operate properly. Various types of thermally conductive materials used for such heat removal have hitherto been described. Thermally conductive materials for such cases exist in two forms: (1) sheet-like materials that are easy to handle, and (2) paste-like materials which are called thermal greases.
Of these, the sheet-like materials (1) are not only easy to handle, they also have an excellent stability. On the other hand, because the contact thermal resistance inevitably increases, the heat-releasing performance is inferior to that of thermal greases. Moreover, because such materials must have a certain degree of strength and rigidity in order to maintain the form of a sheet, they are unable to absorb the tolerances that arise between a component and its housing; hence the component is sometimes destroyed by stresses thereon.
By contrast, thermal greases (2) are not only adaptable to the mass production of electrical and electronic components through the use of dispensing or printing devices, because of their low contact thermal resistance, they also have an excellent heat-releasing performance. However, when the viscosity of the thermal grease is lowered so as to obtain a good dispensing or printing performance, this limits the content of thermally conductive inorganic filler, making it impossible to ensure sufficient thermal conductivity. Hence, heat removal becomes inadequate, as a result of which component malfunction may arise.
This situation has led to the disclosure of even higher performance thermally conductive silicone grease compositions, such as grease-type silicone compositions that combine a specific organopolysiloxane, a thickener such as zinc oxide, alumina, aluminum nitride, boron nitride or silicon carbide, an organopolysiloxane having at least one silicon-bonded hydroxyl group per molecule and an alkoxysilane, thereby suppressing bleeding of the base oil (Patent Document 1); thermally conductive silicone compositions of excellent thermal conductivity and dispensing ability which are obtained by combining a liquid silicone with a thermally conductive inorganic filler having a given thermal conductivity and a Mohs hardness of 6 or more, and a thermally conductive inorganic filler having a given thermal conductivity and a Mohs hardness of 5 or less (Patent Document 2); thermally conductive grease compositions obtained by combining a specific base oil with a metallic aluminum powder having an average particle size of from 0.5 to 50 μm (Patent Document 3); silicone grease compositions in which the loading of aluminum nitride within the silicone grease has been increased by using in admixture two types of aluminum nitride powders of differing average particles sizes (Patent Document 4); and silicone grease compositions that suppress bleedout by increasing the oil viscosity (Patent Document 5). However, thermally conductive silicone grease compositions that can be fully adapted to the increasing performance of electronic and electrical components in use have yet to be achieved.